Depulpers.—The term " depulpers " has been applied to a class of apparatus rendered necessary by the inability of the ordinary filters to completely remove the fine pulpy matters from the juice. They are really nothing more than effective mechanical filters. That of Loynes, made by the Cie. de Fives-Lille, is largely used in other industries besides beet-sugar making. Those of Mariolles and Mesnard are constructed by Cail.
Centrifugals.—Centrifugal hydro-extracting machines, which are described under Cane-sugar and Refining, have been tried for sepaiating beet-juice from the pulp of the grated roots. In practice, however, they are inespable of extracting more than 60-65 per cent. of the juice under the most favourable conditions, and consequently they are not superior to hydraulic presses. Their use in this sphere is virtually a thing of the past.
Maceration.—The shortcoming of the expression processes gave an impetus to experiment in other directions, and notably with regard to the dissolving and displacing powers of water when applied to the pulp. One of the earliest plans based upon these principles was the maceration system of Schutzenbaoh, illustrated in section in Fig. 1301. The essential parts consist of round sheet-iron vessels a, the bottom b of each being made sloping towards one side, where the liquid can be completely drawn off by taps c. If the tap c is closed, the liquid rises in the tube d, and flows thence by a lateral pipe into a second similar vessel placed at a lower level. Above the bottom b, is a false bottom 8, furnished with a metallic, strainer, which retains the solid pulp while the juice escapes. At the top, in f, is a second similar strainer, formed in two pieces, and easily removable. The vertical bars g suspended from e are for breaking up the pulp, and preventing its making a simple rotation, under the influence of the mechanical agitator 11, attached to the axis aud actuated by the bevel-wheels k 1. The same axis carries cleaning-brushes m, which keep the orifices of the upper grating clear for the passage of air and water ; and a similar set perform the same function for the lower strainer. In working, each vessel receives at first a little juice (except at starting, when the juice is replaced by water); the pulp is then introduced, the agitator being meantime kept in motion, or the densest pulp would fall to the bottom, and soon choke the strainer. The speed. of the agitator must be carefully regulated : too rapid movement
would create a large quantity of froth ; too slow would reduce the rapidity of the maceration, and therefore the effective capacity of the apparatus. A speed of 20-24 turns a minute would seem to give the best results. Later, when the juice is partly expressed, the agi tator may be left at rest ; the ligne ous portion of the cells, being lighter than the water, remains on the sur face, and has no longer a tendency to choke the metallic diaphragm.
Uofortunately, whatever precau tions are taken, a large proportion of pulp always finds its way tlarough the strainer, and these solid matters render the defecation more difficult and imperfect, in consequence of the large quantities of scum to which they give rise. This inconvenience is partially remedied by passing the juice, on its exit frorn the macera tion battery, and before defecation, into another vessel, whose strainers serve to detain some of the ligneous matters held by the juice. With the same object, it is well not to reduce the root to too fine a pulp ; but it is necessary to avoid extremes in either direction, as a too coarse pulp will not be com pletely exhausted, and will thus cause a loss of sugar. The process is only suitable for use where fuel is abundant and cheap, in consequence of the very large quantity of water added, amounting in all to 3-4 times the weight of the root. It is therefore more applicable to rich than to poor juice. The cost of erection is moderate. Thus, for a factory taking 50 tons daily, the outlay would be :—Rasping-machine, 180/. ; macerating-battery complete, 600/. ; press, 200/. ; steam-engine, 8 H.P., 200/. ; total, 1180/. The expenses attending the extraction of the juice would be :-6000 tons of beet at 19s., 5700/. ; transport and washing, 160/. ; interest at 10 per cent., 180/. ; repairs, strainers, brushes, &e., 120/. ; wages of 24 workrnen, 134/. ; washing the cloths, &e., 14/. ; fuel for the steam-engine, 105 tons of coal, 150/. ; fuel to evaporate 35 per cent. of water, 420 tons coal, 605/. ; total, 7063/. The yield is 89 per cent. of juice, or 5034 tons in the season. The cost price is therefore 31s. a ton.